1. Summary and outcome of the 1st LIU-HL-LHC brainstorming meeting (24 th June 2011) Mike Lamont This event is jointly organized by the HL-LHC and LIU projects (Lucio & Roland) to try and find solutions to the present discrepancy between the estimated needs of the LHC and the possibilities of the upgraded injectors.

2. Contributions 30/3/12 Beam characteristics at collision energies for the main HL-LHC scenarios: Fundamental reasons for each beam parameters Oliver Bruning Estimated beam characteristics from the upgraded injectors at 450 GeV: Fundamental limitations Roland Garoby Minimum turnaround time for the LHC at 7 TeVMike Lamont Impact on luminosity of Turn around time, Run time etc.Roland Garoby Turnaround time in previous colliders (RHIC, TEVATRON, HERA)Oliver Bruning Bunch spacing, pile up and all thatFrank Zimmermann Ideas from/for the SPSBrennan Goddard Low transition energy opticsYannis Papaphilippou Possible increase of bunch intensity in the SPS for HL-LHCElena Chapochnikova Single bunch intensity limit in the LHCElias Metral A few considerationsStephane Fartoukh Warning – many updates since then…

3. Performance goals 30/3/12 Levelled peak luminosity5 x 10 34 cm -2 s -1 Virtual peak luminosity> 10 x 10 34 cm -2 s -1 Integrated luminosity200 to 300 fb -1 per year Total integrated luminosity3000 fb -1

4. Levelling 30/3/12 HL-LHC will use leveling leveled luminosity is defined: 5x10 34 cm -2 s -1 “ATS optics” solution for beta* < 30 cm Level for T level and then take another 3 hours

5. Illustration 30/3/12 kt Level [h] T decay [h] Virtual lumi Levelled lumi Fill length [h] Int lumi per fill [fb-1] Required Efficiency 24.131e355e347.11.1375% 47.032e355e34101.6563% Assuming: 1.8 10 11 ppb @ 25ns or 3.5 10 11 ppb @ 50ns (≈ 5 10 14 p/beam) 3 hours after the end of levelling with natural luminosity decay 2 high luminosity IPs Only luminosity burn Perfect levelling Required overall efficiency to get 250 fb -1 /year…

6. Operational efficiency Assume 150 days/year – Need 150 – 220 fills per year 3 hour minimum turnaround and 5 hour average turnaround - seem like reasonable numbers Can play the usual games but will need high operational efficiency (65 to 75%) and an average turnaround of the order of 5 hours. – Watch double counting Clear that pushing the total beam current and k is going to help – E.g. k = 5 with 6x10 14 p/beam What k’s are within reach? 30/3/12

7. LHC 2011 30/3/12 Mean = 5.4 hours

8. Turn arounds elsewhere 30/3/12 OBOB

9. 25 ns50 ns Protons per bunch 2.0e113.3e11 Number of bunches28081404 Protons per beam5.6e144.6e14 Beam current [A]1.020.84 X-angle [microrad]475520 Beam separation [s]10 Beta* [m]0.15 Norm. emittance 2.53.0 Bunch length [cm]7.5 Geom. reduction F0.37 Peak lumi7.4e348.4e34 Virtual peak20e3422.7e34 Levelled5e34 k44.5 Pile-up95190 HL baseline target OBOB

10. Comments OK for HL goals with 25 ns Stick numbers into the levelling formulae Both scenarios with 60% efficiency on 150 day year give 250 fb -1 but we note the pile-up of 190 with 50 ns – Level at 2.5 x 10 34 cm -2 s -1 (OB)… 30/3/12

11. Pile-up 30/3/12 Experiments preparing for = 100 (68% of bunch crossings will have between 100 +/- 10 events)

12. Reminded of limits 30/3/12 RA

13. 30/3/12 25 ns50 ns Protons per bunch1.7e112.5e11 Number of bunches28081404 Protons per beam4.8e143.5e14 Beam current [A]0.860.64 X-angle [microrad]480520 Beam separation [s]10 Beta* [m]0.15 Norm. emittance2.53.5 Bunch length [cm]7.5 Geom. reduction F0.370.4 Peak lumi5.3e345.2e34 Virtual peak14e3411e34 Levelled5e34 k2.82.5 Pile-up95190 APPROXIMATE LIU BASELINE AS OF LAST JULY (OB & RG) OB

14. LIU baseline 25 ns short of HL goals – 60% efficiency on 150 days gives 225 fb -1 50ns requires > 80% machine efficiency to even get close 30/3/12 Could take this set as the lower limits of acceptable parameters and rely on the ingenuity of LHC personnel to push peak performance and operational efficiency

15. Oliver’s conclusions CRAB cavities are a vital ingredient for HL-LHC. Without them we will fall short of 250 pb-1 goal (k ≥ 4). – CC are the best tool for compensating geometric reduction factor (LRBB wires perhaps partially) (flat beams [SF]) Given equal bunch parameters, 25 ns case is clearly better than 50 ns (assuming there is no electron cloud limit for 25ns!) If LHC is limited by total beam current, 50 ns offers larger performance reach (higher virtual luminosity for equal lifetime) – 50ns schemes benefit from double batch injection & higher brightness Rather then lowering the bar for project goals, I would stick to challenging (ideal) goals [while underlining that there is a risk associated to it (like CC & Nb3Sn for HL)] and to pursue novel schemes (e.g. feedback systems etc.) 30/3/12

16. Frank’s conclusions No beam-beam limit Limit on total beam current in LHC [& SPS] due to several systems (RF, dump, vacuum, collimator robustness, machine protection, RP, …) at ultimate value Single bunches > 3e11 ppb with 2.5 micron emittance have been accelerated in the SPS We can get a factor 2 higher peak luminosity with 50 ns spacing at the same current In addition we may get smaller emittance at 50 ns – additional gain in peak luminosity? – pile up replaces beam-beam as HL-LHC constraint Leveling works! 30/3/12

17. LIU Estimated beam characteristics from the upgraded injectors 30/3/12

18. Strategy Increased brightness: – LINAC4 – Booster injection energy – PS injection energy – Higher brightness measures in PSB, PS and SPS Emittance conservation – Measurements, understanding, low gamma T Consolidate for reliability and longevity 30/3/12

19. Estimates NB: Numbers refer to injection into LHC Assume all necessary improvements in injectors are made and work as foreseen Budget - assumptions made: – PSB inj-extr: 5% emittance blowup, 5% beam loss – PS inj-extr: 5% emittance blowup, 5% beam loss – SPS inj-extr: 10% emittance blowup, 10% beam loss (including scraping) – LHC inj-flat top: 10% emittance blowup, 10% beam loss 30/3/12

20. R.G. 20 Brainstorming – 24/06/2011 Beam parameters at LHC injection [50 ns] Beam Parameters at 7 TeV ?? H/V transverse emittances [mm.mrad] Bunch intensity within constant longitudinal emittance [x10 11 p/b] Nominal performance Baseline (estimated limit of SPS) Baseline (estimated limit of SPS) Stretched: (estimated limit of SPS injectors) Stretched: (estimated limit of SPS injectors)

21. R.G. 21 Brainstorming – 24/06/2011 Beam parameters at LHC injection [50 ns] Beam Parameters at 7 TeV ?? MD: single bunch with low  t MD: double PSB batch H/V transverse emittances [mm.mrad] Bunch intensity within constant longitudinal emittance [x10 11 p/b] Q2/2011 Nominal performance Baseline (estimated limit of SPS) Baseline (estimated limit of SPS) Stretched: (estimated limit of SPS injectors) Stretched: (estimated limit of SPS injectors)

22. R.G. 22 Brainstorming – 24/06/2011 Beam parameters at LHC injection [25 ns] Beam Parameters at 7 TeV ?? H/V transverse emittances [mm.mrad] Bunch intensity within constant longitudinal emittance [x10 11 p/b] Nominal performance Baseline (estimated limit of SPS) Baseline (estimated limit of SPS) Stretched: (estimated limit of SPS injectors) Stretched: (estimated limit of SPS injectors)

23. R.G. 23 Brainstorming – 24/06/2011 Beam parameters at LHC injection [25 ns] Beam Parameters at 7 TeV ?? MD: double PSB batch H/V transverse emittances [mm.mrad] Bunch intensity within constant longitudinal emittance [x10 11 p/b] MD: single bunch with low  t Nominal performance Baseline (estimated limit of SPS) Baseline (estimated limit of SPS) Stretched: (estimated limit of SPS injectors) Stretched: (estimated limit of SPS injectors)

24. 25 ns after LIU upgrade Fundamental limit: space charge in PS Limit is 2.3e11 p+/b in 3.6 um at SPS extraction (1.6e11 in 2.3 um) 30/3/12 Brennan at Chamonix

25. 50 ns after LIU upgrade Limited by longitudinal instabilities in PS and SPS, and by brightness in SPS Limit is 2.7e11 p+/b in 2.7 um at SPS extraction (closer to HL-LHC requirement) 30/3/12 Brennan at Chamonix

26. Table of dreams? 25 ns Ib [e11]Exy [um]scaled Ib^2/Exy HL-LHC target (LHC flat-top)2.02.51.00 LIU scenario (SPS extraction) LIU baseline (>LS2)2.33.60.92 + "stretch" blowup/losses (>LS3)2.33.31.00 + PS  Q to -0.32, PSB DQ to -0.31 (>LS3) 2.12.31.20 50 ns I [e11]Exy [um]scaled Ib^2/Exy HL-LHC target (LHC flat-top)3.33.01.00 LIU scenario (SPS extraction) LIU baseline (>LS2)2.7 0.74 + "stretch" blowup/losses (>LS3)2.82.50.86 + PS longitudinal stability 3.7e11 (>LS3)3.43.21.00 + SPS  Q to -0.17 (>LS3) 3.42.81.14 30/3/12 Brennan at Chamonix

27. Stretching “A number of optimistic assumptions are necessary for reaching the HL-LHC figures, concerning the success of measures against space charge, instabilities, e-cloud and to minimize beam loss and emittance growth.” 30/3/12

28. Invitation to further reading Momentum slip stacking - Elena Low gamma T optics in SPS – Yannis Exotic SPS scrubbing Longer bunches at SPS2LHC transfer Bunch merging in SPS/LHC Different working points in SPS Low gamma T: increase instability thresholds...still many issues to address (multi-bunch, RF volts, longitudinal transfer to LHC,...) Alternative filling patterns for LHC if limited by total SPS current What about halving the bunch length in the LHC? (SF) Pacman versus micro-batches (SF) What to do at the beginning of the coast if natural peak > levelled luminosity value? (SF) 30/3/12

29. Conclusions Posted HL parameters are outside: LIU baseline and LHC intensity limits - but not ridiculously so… 250 fb -1 /year is challenging – Requires high availability and efficient operation – Very effective levelling is implied Push k - stretch LIU… 30/3/12